1. Field of the Invention
The present invention relates to a radio power supply technique and, more particularly, to a radio power-fed terminal, system, and method concerning a method of selecting a frequency to be used for radio power supply.
2. Description of the Related Art
A radio power supply system has been known, which comprises a microwave transmission terminal for radio power supply including a microwave transmission unit and a radio communication unit, and a power-fed terminal which includes a radio power supply unit and a radio communication unit and wirelessly receives power. Use of this system enables information transmission/reception and radio power supply (wireless transmission) of energy (JP-A 2004-127276 (KOKAI)).
The conventional radio power supply system performs radio power supply using a microwave having a specific frequency. For example, when a frequency of 2.4 GHz in the ISM band is used, it may interfere with radio communication of, e.g., wireless LAN. The number of frequencies available in radio communication is finite, and many frequencies are already assigned for radio communication. It is therefore difficult to ensure a frequency for radio power supply.
To ensure a frequency, a cognitive wireless technique has been developed. In cognitive radio communication, it is detected whether an already assigned frequency is being used or not. Radio communication is performed using an available frequency that is not being used. This reduces interference with radio communication.
The cognitive radio communication technique may be applied to radio power supply. If there are a plurality of available frequencies, a frequency optimum for radio power supply must be selected. However, no method has been disclosed so far.
The conventional radio power supply system performs radio power supply using a microwave having a specific frequency, as described above, and this may cause interference with radio communication. Although an available frequency may be used, the problem of the method of selecting a frequency optimum for radio power supply still remains unsolved.